1. Field of the Invention
This invention pertains generally to electrical sockets, receptacles, plugs and extension cords, and more particularly to an electrical connection safety apparatus which prevents fires and electrical shocks due to overload faults caused by defects associated with AC electrical appliances, outlets and cords and by improper use of electrical extension cords. The electrical connection safety apparatus of the invention senses the current rating of electrical cords when the cords are plugged into an electrical socket, and disconnects the power to the socket and cord when the load current through the socket and cord exceeds the cord current rating. The electrical connection safety apparatus may be used with conventional electrical cords and sockets, and will reset itself whenever a cord is unplugged or removed from a socket.
2. Description of the Background Art
The use of electrical "extension" cords is well known and is widely practiced in residential settings to allow power to reach electrical appliances which are remote from wall-mounted AC electrical outlets, sockets or receptacles. Electrical extension cords for use at relatively low current ratings are widely available, and a variety of power strips and multiple receptacle devices are often used in conjunction with extension cords to allow multiple appliances to draw power from a single extension cord. Because of the ease and convenience provided, extension cords have been and likely will continue to be overused as semi-permanent extensions of household electrical systems.
While the advantages provided by extension cords are well known, there are also important disadvantages associated with extension cord use. Particularly, a large percentage of residential and commercial fires are due to electrical causes involving extension cords. Persons using extension cords often lack sophistication with regard to electrical properties of the appliances, extension cords and receptacle devices. Thus, users of extension cords often select and purchase cords having the smallest physical size and position the cords under carpets or behind drapes in order to minimize visibility of the cords. In situations where the current flowing through an extension cord exceeds the cord's current rating, overheating of the internal conductors occurs which can result in the burning of cord insulation and materials adjacent to the cords, resulting in fires.
The fire risk associated with extension cord use has not been abated even though electrical safety is widely regulated by state, local and national government codes and regulations. For example, in the United States, the National Electric Code or NEC provides building safety codes which regulate the various parts of building electrical systems, including switches, lighting fixtures, wiring, outlets, circuit breakers, fuses and the like. However, NEC regulations essentially stop at the electrical outlet, and electrical appliances and extension cords are not regulated by building electrical codes. Local government ordinances generally require that all electrical appliances, extension cords and like items be approved by Underwriter's Laboratories or "UL." However, while building electrical systems and the appliances and cords used therewith are separately regulated to ensure safety, there are generally no regulations, ordinances or guidelines in place to provide for safety of the overall electrical system together with connected cords and appliances. Thus, a user of an electrical system can assemble one or more extension cords and appliances with a building electrical system, each of which complies with government codes, to achieve an arrangement which is unsafe and presents a risk of fire and electric shock.
The above problem is illustrated by the following scenario. In the United States, a typical wall-mounted AC electrical outlet or receptacle for residential use is rated to handle fifteen amperes of current. Electrical protective devices such as circuit breakers and/or fuses are generally associated with the electrical outlet and will "trip" or disconnect the outlet in the event that a current overload through the outlet occurs. A user connects a standard electrical extension cord rated for ten amperes of current to the outlet, and then connects a multiple receptacle power strip to the extension cord. The user then connects three electrical appliances to the power strip, with each appliance operating normally with a five ampere current load. In the event that all three appliances are activated or turned on simultaneously, each appliance will simultaneously draw a five ampere current load, resulting in fifteen amperes of current flowing through the ten ampere extension cord. Since the current rating of the cord is exceeded, the cord conductors can overheat and burn the cord insulation and adjacent materials, and thus cause a house fire. The circuit breaker or other safety device which protects the outlet will not trip or otherwise interrupt the current flow because the current through the outlet has not exceeded the outlets fifteen ampere threshold. Thus, even though the building electrical system, extension cord and appliances each comply with safety codes, a fire can result from their use, and the fire is not avoided by the current overload protection provided by the circuit breaker.
Other current overload faults can develop in residential situations wherein the conventional overload protection provided by circuit breakers will also fail to prevent a fire. Electrical appliances such as televisions, refrigerators, toasters, computers and the like can, and often due, develop internal faults that cause a "hot spot" within the appliance. For example, in appliances wherein an electric motor drives rotating or moving parts, such as in refrigerators, the bearings or bushings wear and lose lubrication, and the electric current needed to operate the motor increases in order to overcome the friction. When such an appliance failure occurs, the current load drawn by the appliance will include the normal operating current together with fault-induced current. This total current can exceed the current rating of the electrical cord of the appliance but still be insufficient to trip the protective circuit breaker, and thus result in a fire as the cord overheats. Additionally, many appliances include internal combustible materials which can ignite as a result of current overload.
Still another situation in which an overload fault can result in a fire involves electrical outlets themselves and the circuit breakers or fuses installed to protect them from overload situations. As noted above, in the United States, residential electrical outlets are typically rated for fifteen amperes of current. For various reasons, circuit breakers or fuses are often inadvertently installed which have higher current trip levels, such as twenty amperes, than the electrical outlet current rating. In such situations the electrical outlets themselves can overheat and cause a fire.
Various devices are known for protection against ground faults associated with appliances and cords, such as ground fault circuit interrupters and ground fault shields. However, these devices offer no protection in current overload fault situations. Presently, there are no available devices or systems which can remedy the aforementioned problems associated with current overload faults in electrical appliances, extension cords or outlets.
Accordingly, there is a need for an electrical connection safety apparatus which provides protection against overload faults in electrical systems which could otherwise result in a fire. The present invention satisfies this need, as well as others, and generally overcomes the deficiencies found in the background art.